Insertion of the trocar into the body is the presupposition for carrying out an endoscopic diagnosis or therapy in the abdomen. After penetrating the body wall with the trocar, the trocar pin is removed from the trocar sleeve, which stays in the abdominal wall, and an endoscope or endoscopic instrument is inserted through the sleeve. Before introducing the trocar, a pneumoperitoneum is established, using CO.sub.2 gas, to achieve a distance between the abdominal wall and the organs. Upon inserting the trocar through the abdominal wall the sharp trocar tip may injure the organs if it penetrates too deeply by not working cautiously and carefully.
According to the state of art (FIG. 1) different shapes of trocar tips are in use. For example, conical, three-faced-pyramidal with sharp edges, and also conically threaded for screwing-in are sometimes used. To reduce risk of injury EP 0265 193 describes a protective sleeve, surrounding the trocar tip (FIG. 2). The sleeve snaps forward, shielding the sharp tip, after the trocar has penetrated the abdominal wall. For penetrating the tissue, there is still a relatively large force to be expended, and the safety mechanism does not come into play until the tip has fully entered the abdomen. The forward jumping of the sleeve only avoids injury occurring after pushing the trocar forward into deeper regions, due to the suddenly reduced resistance. Another method is described in EP 0135 364 B 1 dealing with a triple bladed knife, which moves forward out of the trocar sleeve to cut through the body wall. The trocar is pushed into the cut and then the blade is retracted into the body, the cone is pressed back by the body tissue and the blades cut. After having penetrated the body wall, the cone snaps forward and protects the blades in its slots. This method also has the disadvantage that it needs a rather high penetration or cutting force and entails the same dangers as the pyramidal trocar.
An object of the present invention is to avoid the sudden further penetration of the trocar due to the force applied by the operating surgeon, and reduce the risk of injuries after having penetrated the body wall. The force acting on the trocar has to be reduced, to avoid the sudden dangerous movement.